Various oxazolidinone derivatives having antimicrobial activity were known in the art, as disclosed, for example, in U.S. Pat. No. 6,255,304 (Patent Document 1), U.S. Pat No. 6,218,413 (Patent Document 2), U.S. Pat. No. 6,362,189 (Patent Document 3), U.S. Pat. No. 6,342,513 (Patent Document 4), U.S. Pat. No. 6,537,986 (Patent Document 5), WO2000/032599 (Patent Document 6), WO99/24428 (Patent Document 7), WO97/10223 (Patent Document 8), WO97/09328 (Patent Document 9), U.S. Pat. No. 5,523,403 (Patent Document 10), WO95/07271 (Patent Document 11), WO2004/014392 (Patent Document 12), U.S. Pat. No. 6,956,040 (Patent Document 13), U.S. Pat. No. 6,734,307 (Patent Document 14), WO2002/006278 (Patent Document 15), WO2003/008389 (Patent Document 16), WO2003/007870 (Patent Document 17), WO2005/058888 (Patent Document 18), WO2004/096221 (Patent Document 19), EP697412A (Patent Document 20), WO2000/027830 (Patent Document 21), Japanese Patent Application Publication 11-322729 (Patent Document 22), Japanese Patent Application Publication 9-221476 (Patent Document 23), WO95/34540 (Patent Document 24), WO2003/002560 (Patent Document 25), WO99/64417 (Patent Document 26), EP657440B (Patent Document 27), WO2005/019213 (Patent Document 28), Japanese Patent Application Publication 2005-524660 (Patent Document 29), U.S. Pat. No. 6,239,152 (Patent Document 30), U.S. Patent Application Publication No. 2005/4174A1 (Patent Document 31), Japanese Patent Application Publication 2003-513885 (Patent Document 32), WO99/37630 (Patent Document 33), Japanese Patent Application Publication 2003-519141 (Patent Document 34), Japanese Patent Application Publication2000-204084 (Patent Document 35), Japanese Patent Application Publication 11-322729 (Patent Document 36), Japanese Patent Application Publication 11-158164 (Patent Document 37), WO2004/101552 (Patent Document 38), WO2004/026848 (Patent Document 39), WO2003/11859 (Patent Document 40), WO2004/002967 (Patent Document 41).
Particularly, (S)-N-[[3-[3-fluoro-4-(4-morpholinyl)phenyl]-2-oxo-5-oxazolidinyl]methyl]acetamide (“linezolid”), as disclosed in WO95/07271 (Patent Document 11), has a potent antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococci (VRE) and it has been approved and marketed as a VRE anti-infectious drug.
Triazacycloheptane derivative was also known but its antimicrobial activity and use as an intermediate were not disclosed (Patent Document 42, Patent Document 43, Patent Document 44, Patent Document 46, Non-patent Document 1).
Also, the applicant has filed a patent application for oxazolidinone derivatives having 7-membered hetero ring as an timicrobial agent (Patent Document 45).
[Patent Document 1] U.S. Pat. No. 6,255,304
[Patent Document 2] U.S. Pat. No. 6,218,413
[Patent Document 3] U.S. Pat. No. 6,362,189
[Patent Document 4] U.S. Pat. No. 6,342,513
[Patent Document 5] U.S. Pat. No. 6,537,986
[Patent Document 6] WO2000/032599
[Patent Document 7] WO99/24428
[Patent Document 8] WO97/10223
[Patent Document 9] WO97/09328
[Patent Document 10] U.S. Pat. No. 5,523,403
[Patent Document 11] WO95/07271
[Patent Document 12] WO2004/014392
[Patent Document 13] U.S. Pat. No. 6,956,040
[Patent Document 14] U.S. Pat. No. 6,734,307
[Patent Document 15] WO2002/006278
[Patent Document 16] WO2003/008389
[Patent Document 17] WO2003/007870
[Patent Document 18] WO2005/058888
[Patent Document 19] WO2004/096221
[Patent Document 20] EP Patent No. Publication EP697412A
[Patent Document 21] WO2000/027830
[Patent Document 22] Japanese Patent Publication 11-322729
[Patent Document 23] Japanese Patent Publication 9-221476
[Patent Document 24] WO95/34540
[Patent Document 25] WO2003/002560
[Patent Document 26] WO99/64417
[Patent Document 27] EP Patent No. 657440B
[Patent Document 28] WO2005/019213
[Patent Document 29] Japanese Patent Publication 2005-524660
[Patent Document 30] U.S. Pat. No. 6,239,152
[Patent Document 31] US Application Publication 2005/4174A1
[Patent Document 32] Japanese Patent Publication 2003-513885
[Patent Document 33] WO99/37630
[Patent Document 34] Japanese Patent Publication 2003-519141
[Patent Document 35] Japanese Patent Publication 2000-204084
[Patent Document 36] Japanese Patent Publication 11-322729
[Patent Document 37] Japanese Patent Publication 11-158164
[Patent Document 38] WO2004/101552
[Patent Document 39] WO2004/026848
[Patent Document 40] WO2003/11859
[Patent Document 41] WO2004/002967
[Patent Document 42] UK Patent No. 1543081
[Patent Document 43] EP Patent No. 358749
[Patent Document 44] U.S. Pat. No. 4,801,706
[Patent Document 45] International Application PCT/JP2007/057060 (WO2007/114326)
[Patent Document 46] Japanese Patent Publication 2-503321
[Non-patent Document 1] Dissertationes Pharmaceuticae et Pharmacologicae (1972), 24 (4), 385-390